This invention relates to cross-linkable polymeric compositions particularly suitable as insulating coatings for electric wires, cable, and other electrical conductors.
Polymeric insulating compositions should be flame retardant, and also moisture and heat resistant. Most electric insulating coatings have a tendency to undergo a change of color called "staining". Staining can occur over a period of time as a result of aging.
The prior art discloses several different cross-linkable polymeric compositions suitable as insulating coatings, however the problem of staining, and its solution have not yet been addressed satisfactorily.
U.S. Pat. No. 3,979,356 to Walters discloses a polymeric composition with dielectric properties suitable as an electrical insulator, which comprises an ethylene-vinyl acetate copolymer, hydrated alumina, and a silicone elastomer. The copolymer is cross-link cured to a thermoset state by means of a free radical forming organic peroxide.
U.S. Pat. No. 3,553,348 to Betts discloses an electrical insulating composition comprising a cross-linked ethylene copolymer having about 75 to 90% by weight of ethylene, a chlorine-containing polymer and a filler of magnesium silicate having a platelike structure coated with an alkoxy silane.
U.S. Pat. No. 3,832,326 to North et al discloses an electrical conductor composition comprising a cross-linkable ethylene-vinyl acetate polymer, one or more silanes, and one or more hydrated inorganic fillers.